A high-temperature resistant polyamide can be obtained by polycondensation of an aromatic dicarboxylic acid or an aromatic diamine, and has a semi-aromatic and semi-crystalline structure. High-temperature resistant polyamide has considerably higher temperature resistance as compared to general polyamide products, and thus can be used in various fields requiring high-temperature resistance.
Examples of typical high-temperature resistant polyamide include PA4T, PA6T, PA9T, PA10T, PA11T, PA12T, and the like. For a high-temperature resistant polyamide prepared from a long chain diamine having nine carbon atoms or more, a homopolymer, or a copolymerized polymer prepared from a small amount of comonomer (dicarboxylic acid or diamine) may be used. Typically, for PA4T and PA6T, the homopolymer has a very high melting temperature, thereby makes it difficult to process the homopolymer.
In order to solve this problem, a large amount (several dozen %) of comonomers can be added to enhance melt processability. Examples of the comonomers for PA6T may include short chain and long chain aliphatic diamines, cyclic aliphatic diamines, branched aliphatic diamines, short chain and long chain aliphatic dicarboxylic acids, cyclic aliphatic dicarboxylic acids, branched aliphatic dicarboxylic acids, and the like. For PA6T, common comonomers may include adipic acid, isophthalic acid, and the like.
In a high-temperature resistant polyamide product for use as an LED reflector requiring excellent optical characteristics and discoloration resistance, a cyclic aliphatic dicarboxylic acid may be used instead of an aromatic dicarboxylic acid in order to produce products having excellent resistance to light/heat, or a monomer capable of enhancing glass transition temperature (Tg) in order to inhibit deterioration in physical properties of polyamide products at high temperature may be copolymerized. However, such copolymerization cannot prevent discoloration of polyamide exposed to air at high temperature.
Due to such drawbacks, high-temperature resistant polyesters may be used instead of high-temperature resistant polyamides for products in which discoloration resistance is an important physical property. However, polyesters are generally inferior to high-temperature resistant polyamides in terms of heat resistance. Further, irrespective of good discoloration resistance, polyesters have undesirable hydrolysis property and moldability under humid conditions.
Therefore, there is a need for a crystalline polyamide resin having better heat resistance and discoloration resistance than existing high-temperature resistant polyamide products and which is capable of improving moldability (crystallization rate), the lack of which is a drawback of polyester products.